FRCPath Part 2—Revision Notes on Aspergillus spp.
(Oxford Textbook of Medical Mycology, Ch 10)
1. Genus at a glance
- > 200 species; > 30 human pathogens—among the most ubiquitous environmental moulds; conidia inhaled daily.
- Characteristic aspergillum (asexual conidial head); despite known teleomorphs, the 2012 “one-fungus-one-name” rule retains Aspergillus nomenclature .
- Commercial uses: A. niger → citric-acid & enzyme production; A. oryzae → sake/soy fermentation .
2. Aspergillus Key species, temperatures, toxins & clinical points
Species (complex) | Opt. Temp / Range (°C) | Colony / Microscopy | Major toxin | Salient clinical facts |
A. fumigatus | 37 / 12-65 | Green-blue; columnar uniseriate heads | — | Commonest invasive isolate; ABPA, CPA |
A. flavus | 37 / 12-48 | Green-yellow; radiate uni/bi-seriate | Aflatoxin | Sinusitis, keratitis, aflatoxicosis risk |
A. niger | 37 | Black biseriate heads | — | Otomycosis, onychomycosis |
A. terreus | 25-40 | Beige; biseriate + accessory conidia | Ochratoxin | Intrinsic AmB-R |
A. nidulans | 37 / 2-48 | Green with red-brown cleistothecia | — | CGD infections; AmB-R |
A. versicolor | 22-26 (opt); ≤40 | White→yellow/green; penicillium-like | Sterigmatocystin | Onychomycosis; grows best at room-temp |
A. clavatus | 37 | Long club-shaped vesicle | — | Extrinsic allergic alveolitis (“malt-worker’s lung”) |
EORTC definitions
Proven:
- Histologically proven and evidence of tissue damage
- Growth of aspergillus from a sterile site
Probable
- Host factor: neutropenia, transplant, cirrhosis, HIV, chronic lung disease, steroids, infleunza pneumonitis
- Presence in the lower respiratory tract: cytology, microscopy or growth OR GM >0.8 in BALF, >0.5 in serum
- Radiological factors: nodule, air crescent, cavity, wedge/segmental/lobar consolidation, tracehobrachial eschar or ulcer.





Green-yellow radiate, compare to A. fumigatus

Cinnamon colored, columnar

3. Epidemiology & reservoirs
- Conidia in soil, rotting vegetation, damp building materials (wallpaper, concrete, pipe-lagging, carpets, HVAC); hospital construction dust → outbreaks .
- High-risk hosts: prolonged neutropenia, allogeneic-HSCT (~12 %), heart-lung Tx (11 %), CGD, high-dose steroids .
- CPA rising after TB, COPD, sarcoidosis .
4. Pathogenesis (4-step mnemonic I-G-A-T)
1 Inhalation & alveolar deposition
2 Germination when innate immunity fails
3 Angio-invasion → thrombosis, infarction
4 Toxins & hypersensitivity drive allergic / chronic disease
5. Clinical spectrum
Category | Typical entities / notes |
Non-invasive | Otomycosis (A. niger), onychomycosis (A. versicolor), allergic fungal rhinosinusitis |
Allergic | ABPA (≈16 % asthmatics); EAA by A. clavatus; SAFS |
Chronic | CPA continuum: simple aspergilloma → chronic cavitary → fibrosing disease |
Invasive | Acute pulmonary IA ± CNS, eye, skin; sinusitis; mortality 50–85 % |
6. Diagnosis workflow
- Direct / culture: septate 45° branching hyphae; Sabouraud agar 48-90 h.
- Serology & biomarkers:
- Aspergillus precipitins (IgG)—best single test for CPA/ABPA support .
- Galactomannan ELISA / LFD (false-pos with β-lactams) .
- (1→3) β-D-glucan (pan-fungal) .
- PCR on blood/BAL; combine with GM for ↑ sensitivity .
- Imaging: HR-CT halo sign → air-crescent; MRI for CNS/sinus.
- Histology/BAL/biopsy for EORTC “proven” disease.
7. Antifungal susceptibility & resistance
- Azole-R A. fumigatus increasing in Europe (environmental TR34/L98H, TR46/Y121F/T289A).
- Intrinsic AmB-R: A. terreus, A. nidulans.
- Always request MICs on invasive isolates.
8. Management cheat-sheet
Condition | First-line | Key alternatives / notes |
Invasive aspergillosis | Voriconazole | Liposomal AmB; isavuconazole (non-inferior; shortens QT c) |
ABPA | Oral steroids ± itraconazole/posaconazole | |
CPA | Long-term oral triazole; monitor levels | |
Onychomycosis / Otomycosis | Topical clotrimazole ± oral azole | |
Surgical | Resection of solitary aspergilloma; debridement of sinus/CNS masses | |
Supportive: remove colonised lines, taper immunosuppression, give G-CSF if neutropenic.
9. Prognosis & prevention
- IA mortality: 50-60 % (SOT) → 70-85 % (other immunosuppressed). Early targeted therapy improves survival .
- Primary prophylaxis (e.g. posaconazole in AML/allo-HSCT) cuts incidence but monitor for resistance.
- Environmental control: HEPA filtration, positive-pressure rooms, meticulous dust containment during building/refurbishment .
10. High-yield exam pearls
- Columnar uniseriate head + growth to 65 °C = A. fumigatus.
- Accessory conidia → think A. terreus (and AmB-R).
- Galactomannan false-positive with piperacillin-tazobactam or Penicillium.
- Sterigmatocystin ↔ A. versicolor; ochratoxin ↔ A. terreus; aflatoxin ↔ A. flavus.
- Report isolates as “A. fumigatus complex” unless molecular ID performed (≥ 40 cryptic species) .
- Isavuconazole shortens QTc (contrast other azoles).
- Memorise EORTC/MSG 2008 possible/probable/proven definitions—frequent SAQ.
- Environmental reservoirs (damp concrete, carpets, HVAC) explain hospital outbreak questions.
- Room-temperature growth (~25 °C) onychomycosis isolate? Think A. versicolor.